The present invention relates to a filter made of a porous ceramic sintered body to scavenge particulates (fine particles) in fluid, which is represented by a diesel particulate filter.
The diesel particulate filter (DPF), which is a kind of filter of a porous ceramic sintered body, has a honeycomb structure having a large number of through channels (cells) partitioned by partition walls (libs) and passing through along an axial direction, and adjacent through channels are alternatively sealed at the opposite end mutually so that both end surfaces of the filter are clogged checkerwise.
When exhaust gas of a diesel engine is sent from one end surface of this honeycomb structure, exhaust gas containing particulates flows inside from the through channels which are not sealed in an end portion of the end surface, passes through the porous partition walls, and enters into the other through channels which are not sealed in the other end portion of the structure. And, when the exhaust gas passes through the partition walls, particulates in the exhaust gas are caught in partition walls and the purified exhaust gas from which the particulates are removed is exhausted from the other end of the structure.
In a filter of such a principle, there is a close relation among pore diameter of a porous ceramic sintered body composing a filter, scavenging efficiency of particulates, and pressure loss. For example, as shown in the specification of JP-A-5-23512, the fall in the scavenging efficiency cannot be avoided in a filter wherein large fine pores are also present. On the other hand, if the diameter of its fine pores become smaller, the pressure loss increases.
Therefore, the above-mentioned specification discloses a technique to set average pore diameter of a filter in a predetermined range and set standard deviation in distribution of pore diameters to be the predetermined value or less (that is, to make a large number of fine pores having pore diameters of a limited range present as much as possible) to provide a DPF having a low pressure loss and a high scavenging efficiency.
However, as shown in JP-A-5-23512, it is necessary to change qualities of materials, raw materials, a production method, and the like, of a filter from the foundation, thereby adjustment is inevitably required. In addition, there is a problem that it is impossible to produce any kind of filter having any average pore diameter and any distribution of pore diameter according to various kinds of uses, depending upon kinds of particulates, temperature for use, or the like.
The present invention has been made in view of such conventional circumstances and aims to provide a filter made of a porous ceramic sintered body which does not need adjustment on a large scale such as changing properties of material for the filter, which can be made relatively easily, and which can cope with various uses flexibly.
According to the present invention, there is provided a filter made of a porous ceramic sintered body (first aspect of the invention) having a honeycomb structure having a large number of through channels partitioned by partition walls and passing through along an axial direction, characterized in that when a ratio of a pore volume having a diameter of 30 xcexcm or more to a total pore volume, measured by a method of mercury penetration, of the filter is P1(%) and a thickness of said partition wall is T (xcexcm), these satisfy the relationship defined by the following formula:
P1xc3x9710xe2x89xa6T. 
According to the present invention, there is further provided a filter made of a porous ceramic sintered body (second aspect of the invention) having a honeycomb structure having a large number of through channels partitioned by partition walls and passing through along an axial direction, characterized in that when an average pore diameter, measured by a method of mercury penetration, of the filter is D (xcexcm) and a thickness of the partition wall is T (xcexcm), these satisfy the relationship defined by the following formula:
Dxc3x97100xe2x89xa7T. 
Further, according to the present invention, there is furthermore provided a filter made of a porous ceramic sintered body (third aspect of the invention) having a honeycomb structure having a lot of through channels partitioned by partition walls and passing through along an axial direction, wherein when a ratio of a pore volume having a diameter of below 6 xcexcm to a total pore volume, measured by a method of mercury penetration, of the filter is P4 (%) and a thickness of said partition wall is T (xcexcm), these satisfy the relationship defined by the following formula:
(1/P4)xc3x973000xe2x89xa7T. 